A non-aqueous electrolyte secondary battery including a porous protection film arranged between a negative electrode and a positive electrode and containing resin binders and inorganic oxide fillers is disclosed, for example, in patent literature 1. According to such a structure, the occurrence of an internal short circuit is suppressed even if an active material peeled off from the electrode or swarf in a cutting process attaches to the electrode surface at the time of manufacturing.
It is known as a deterioration mechanism of a non-aqueous electrolyte secondary battery that a positive electrode active material of the secondary battery is eluted and precipitates on the negative electrode to form an insulting coating in the case of overcharge. It is also known as another deterioration mechanism that, when a non-aqueous electrolyte secondary battery is overcharged, concentration polarization in which the concentration of lithium ions dissolved in an electrolyte becomes lower at a positive electrode side while becoming higher at a negative electrode side occurs and lithium, which can no longer enter the negative electrode, precipitates on a negative electrode surface in the form of metallic lithium.
Patent Literature 1:
Publication of Japanese Patent No. 3371301